1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to improving communication performance.
2. Introduction
A wireless communication network is deployed over a defined geographical area to provide various types of services (e.g., voice, data, multimedia services, etc.) to users within that geographical area. In a typical implementation, access points (e.g., corresponding to different cells) are distributed throughout a network to provide wireless connectivity for access terminals (e.g., cell phones) that are operating within the geographical area served by the network. In general, at a given point in time, the access terminal will be served by a given one of these access points. As the access terminal roams throughout this geographical area, the access terminal may move away from its serving access point and move closer to another access point. In addition, signal conditions within a given cell may change, whereby an access terminal may be better served by another access point. In these cases, to maintain mobility for the access terminal, the access terminal may be handed-over from its serving access point to the other access point.
As the demand for high-rate and multimedia data services rapidly grows, there lies a challenge to implement efficient and robust communication systems with enhanced performance. To supplement conventional mobile phone network access points, small-coverage access points may be deployed (e.g., installed in a user's home) to provide more robust indoor wireless coverage to mobile units. Such small-coverage access points may be referred to as, for example, femto access points, femto cells, home NodeBs, home eNodeBs, or access point base stations. Typically, such small-coverage base stations are connected to the Internet and the mobile operator's network via a DSL router or a cable modem.
When an access terminal is on a call on a macro system and enters the wireless coverage of a femto access point, hand-in may be triggered to that femto access point. In practice, however, an identifier used to identify the femto access point may be subject to reuse, whereby multiple femto access points within the wireless coverage of the macro system may be assigned the same identifier. For example, there may be a relatively large number of femto access points within the coverage area of any given macro access point. Moreover, it is expected that femto access points may be deployed in an ad-hoc fashion. Thus, the identifiers assigned to these femto access points may overlap (e.g., as a result of individual decisions of homeowners that install the femto access points in their homes).
To resolve ambiguity as to which femto access point is the intended target for a given hand-in operation, a femto access point may employ an uplink (e.g., reverse link) receiver for acquiring signals transmitted by an approaching access terminal. In this way, hand-in preparation operations may be directed only to a femto access point that is close enough to the access terminal to receive signals from the access terminal.
In the event a large number of femto access points under a given macro access point are assigned the same identifier, the macro access point may direct all of these femto access points to attempt to acquire signals (e.g., the reverse link) transmitted by an access terminal that reported the detection of signals from one of these femto access points to the macro access point. The number of deployed femto access points compounds this hand-in problem since, not only are many femto access points being asked to determine if they are the intended target, but due to femto access point density, the number of active call hand-in attempts per access terminal increases.
In addition, in some cases a femto access point may employ additional radio frequency (RF) receivers. For example, a femto access point may employ an uplink receiver for receiving uplink signals from access terminals that connect to the femto access point. In addition, the femto access point may employ a downlink receiver for deriving synchronization from downlink signals received from a nearby macro access point. Such macro-based synchronization may be used, for example, in a case where GPS functionality is not supported or received GPS signals are too weak to acquire synchronization.